In recent years, as a diagnostic imaging technique using an ultrasonic diagnostic apparatus, elastography that visualizes the hardness of a living tissue has been in practical use. In elastography, for example, a stress is applied to a surface of a living tissue by applying and releasing pressure to the tissue with vibration of an ultrasound probe by an operator, and information about strain of the tissue in a living body caused by the stress is calculated from reflected wave data, as harness information.
To calculate information about strain of a tissue (hereinafter, “strain information”) in such an ultrasonic diagnostic apparatus, detection of a displacement of the tissue or a moving velocity of the tissue is required. As a method of calculating strain information, a method in which a displacement of a tissue between adjacent frames is detected based on cross-correlation of reception radio frequency (RF) signals of ultrasonic waves, a method in which a moving velocity of a tissue is detected by Doppler method, and a method in which these two methods are combined have been used.
Moreover, provision of reference information to an observer by displaying the reference information has been practiced for an operator to judge whether the strain information calculated by the method is appropriate. The reference information indicates whether pressure and release to a living tissue has been appropriately performed. For example, a method in which a waveform where the vertical axis indicates a mean moving velocity of a tissue in a frame calculated from reception data and the horizontal axis indicates elapsed time is displayed as the reference information has been known.
However, even by referring to the reference information described above, it has been difficult for an operator to properly determine a frame of which time is the appropriate strain information.